A turbocharger may be provided in an engine to increase engine torque or power output density. The turbocharger may include an exhaust driven turbine coupled to a compressor via a drive shaft. The compressor may be fluidly coupled to an air intake manifold in the engine connected to a plurality of engine cylinders. Exhaust flow from one or more engine cylinders may be directed to a turbine wheel causing the turbine to rotate about a fixed axis. The rotational motion of the turbine drives an impeller (e.g., wheel) of the compressor which compresses air into the air intake manifold to increase boost pressure based on engine operating conditions.
Compressor efficiency influences overall engine performance and fuel consumption. For example, lower compressor efficiency may result in slow engine transient response and higher fuel consumption for both steady-state and transient engine operation. At lighter engine loads, when compressor efficiency is reduced, increased turbocharger lag may result during a tip-in. Additionally, light load operation may result in lower compressor efficiency and compressor surge limits may restrict boost pressure rise at low engine speeds.
Other attempts to address low compressor efficiency include utilizing a variable inlet compressor that utilize guide vanes to direct and adjust flow through an impeller of the compressor. One example approach is shown by Sconfietti et al in EP2024645. Therein, a variable inlet device disposed adjacent the compressor inlet and including a plurality of vanes is disclosed. Each of the vanes is movable between a first position and a second position to control the quantity of fluid that passes to the impeller. Specifically, the vanes are positioned about a center of a wheel device and pivot about an axis parallel with a central axis of the compressor. In a closed position, flow is blocked from passing to the impeller and in an open position, gas may flow between adjacent blades, around the center of the wheel device.
However, the inventors herein have recognized potential issues with such systems. As one example, even in the open position, due to the orientation and pivoting direction of these vanes, flow through the variable inlet device and to the impeller is restricted (e.g., partially blocked). As a result, this type of variable inlet has reduced high end efficiency and constrains the high end flow with flow restricting issues. Further, this type of device does not generate pre-swirl flow for the compressor which may increase compressor low-end efficiency.
In one example, the issues described above may be addressed by a compressor, comprising: an impeller rotatable about a central axis; and an inlet conduit including a variable inlet device (VID) positioned therein, upstream of the impeller, and including a plurality of adjacently arranged blades forming a ring around the central axis with inner surfaces of the blades forming a flow passage through the VID, each of the blades being pivotable, about an axis arranged tangent to the ring, between an open and closed position. In the open position, the blades may have little to no overlapping with one another and the inner surfaces form a wider flow passage with reduced flow restriction. In the closed position, the blades may have increased overlapping with one another at an outlet end of the VID, thereby restricting flow as it passes through the flow passage of the VID. Further, the overlapping of the blades creates a smooth surface with spiral grooves that generates pre-swirl flow to the impeller as intake air flows through the flow passage of the VID. As a result, compressor efficiency is increased in the closed position due to the restricted, pre-swirl flow that is generated by the VID. Compressor efficiency is further increased at higher loads when the VID is in the open position due to reduced flow restriction through the inlet conduit and VID. In this way, compressor efficiency and overall engine performance and fuel economy may be increased across a wide range of engine operating speeds and loads.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.